This invention relates generally to phase locked loop signal generators and more particularly to phase locked loop signal generators for exciting harmonic related transmitters operating over the marine telegraph bands.
Harmonically related transmitters are conventionally utilized for transmission in the 7 discrete frequency bands between approximately 4 and 25 megaHertz covering the seven marine telegraph bands. These transmitters require seven corresponding discrete frequency bands as inputs, the specific input bands being a factor of the specific design of the transmitter.
Historically, the approach taken for exciting these transmitters has been to utilize an internal crystal oscillator or a general purpose signal generator rather than a dedicated signal generator designed for the specific task. In terms of synthesized generators, general purpose signal generators are relatively more expensive and are larger requiring more space than a generator dedicated to the particular task and having design characteristics optimized for the overall system. Many of the general purpose signal generators, although of the phase locked loop type, require several feedback loops. This not only complicates the electronics involved, but also adds to the expense.
Furthermore, many of the general purpose type signal generators by the very nature require several manual inputs from the operator of the system, thereby unnecessarily complicating operating procedures.